Bc. Ball et al., CROP PERFORMANCE AND SOIL-CONDITIONS ON IMPERFECTLY DRAINED LOAMS AFTER 20-25 YEARS OF CONVENTIONAL TILLAGE OR DIRECT DRILLING, Soil & tillage research, 31(2-3), 1994, pp. 97-118
Crop yield and soil conditions under four different tillage regimes we
re monitored over five growing seasons from 1986/1987 to 1990/1991 as
part of a long-running investigation into reduced tillage effects. Two
long-term treatments (direct drilling and conventional mouldboard plo
ughing, dating from 1968) were compared with two begun in 1983: a shor
tterm direct drilled treatment and a treatment consisting of three sea
sons of broadcast sowing plus rotovation and one season of mouldboard
ploughing and straw incorporation. Autumn and spring nitrogen treatmen
ts were also compared. The crop was winter barley except in 1988/1989
when it was oil-seed rape. Straw was removed, often incompletely, by a
mixture of baling, burning and raking, except in the straw incorporat
ion treatment where it was chopped by the harvester. The experimental
site is located on a Cambisol (15% clay in the topsoil) and a Gleysol
(17% clay in the topsoil) in southeast Scotland. For winter barley, gr
ain yields under long- and short-term direct drilling were comparable
but were lower than those under conventional ploughing and drilling ma
inly because of problems associated with straw residues, grass weeds a
nd seedbed compaction. Yield responses to nitrogen were not consistent
ly related to tillage, although uptake of nitrogen in the grain was fr
equently least in the direct drilled treatments. soil aeration, streng
th and structure were more favourable under ploughing than under direc
t drilling. Bulk density and soil strength did not show any long-term
progressive changes in the long-term direct drilled treatment. Weather
and drainage status varied markedly between seasons and determined th
e number of available workdays during the harvesting and tillage perio
d. Available workdays influenced crop responses to reduced tillage mor
e than soil type or physical condition. In some seasons workdays were
insufficient to permit the high standard of management necessary for s
uccessful reduced tillage, especially direct drilling. Due to this red
uction in management opportunities some direct drilled plots became so
infested with soft brome (Bromus mollis L.) that oil-seed rape was gr
own in 1988/1989 as a break crop.